Beam to Column Pinned Connection

[sunyaer]

There is a challenge task to design a steel transfer beam to support a few storey concrete hollow block masonry wall(190 thick)above. These masonry walls above are load bearing ones, giving a total force of 5,000KN on the beam. The beam spanning 8 meter will be supported on two steel columns, the reaction on one column would be around 2,500KN (factored). The initial size of the column is W250x115, while the beam is W760x484. This frame is in a lateral shear wall system, so the beam in question is laterally supported by the diaphragm. However, the columns in question will have to be braced by the beam or by other method.

The height of the columns is 5.2 meter (from base plate to top of the supported beam,the far end of the columns is considered pinned connection with base plate, although 4 anchor bolts will be used to comply with code for erection safety.)

There are some constraints that make us to not increase the size of the columns. This gives rise to finding a solution for a beam to column pure pin connection, which transfers no moment from the beam to column. If this could be achieved, a column of W250x115 with effective length of about 4.6 meter would support an axial load of 2,500KN.

Some have suggested a beam to column pinned connection like that in the attachment. Do you have experience using similar pinned connection to transfer a magnitude of an axial load of about 2,000 KN to 3,000 KN without considering moment? If a certain level of moment which would be transferred from beam to column, how to consider the magnitude? (Let's assume a 4 inches wide bearing plate as shown in the attachment is used.)

The design uses Canadian code.

Thank you in advance.

 

[Agent666]

Whats the 0.85 factor supposed to represent in reducing the moment out of interest? (or are you saying its a reduction on the capacity?)

If you are worried about bending the web, then you could always weld or fit a backing plate on the far side. If you have the horizontal stiffener on the backside as per your last sketch at the top and bottom of the angles then this potentially prevents or restrains a lot of the web bending

I still don't think the [] shaped weld is that great for transferring moment considering where the moment/shear is applied between the two [ shaped welds. The highest stresses are out on the tips of the [ shaped weld, the weld group under a moment/shear from the connection angle is under both a major, minor and torsional moment and a direct vertical shear (considering where the forces are applied and where the centroid of the weld group is located some distance orthogonal/sideways from the beam web). If your numbers show it works and you are happy with it then I guess it works. I just wanted to make sure you have checked this in enough detail as once the weld fails the connection has little redundancy left, it is a scenario where I can see it just unzipping if it has insufficient strength at the critical top return adjacent the beam web.

Spanner or impact wrench can be used as access might dictate. see

https://en.wikipedia.org/wiki/Podger_spanner

for a picture of one. As far as I'm aware there is no requirement to use an impact wrench to get to the snug tight condition, its achievable by hand.

 

[sunyaer]

The 0.85 factor reduces the moment. Please see in the attached picture.

The [] shaped weld is actually from our design handbook. Is the table not considering moment due to eccentricity of the shear transferred? The table gives capacity up to 3,000KN.

I didn't do a detailed calculation checking the welds for moment, shear and torsion. The connection engineer will design the connection anyway. I've heard many senior engineers saying this.

In my opinion, for this important connection it's worth checking it when designing the main frame. I am thinking of modeling it in a finite analysis program to check the stresses.

For the bolting to column web option, there is a concern of requiring greater level of accuracy of the length of the beam assembly for fitting.

 

[sunyaer]

This is the [] shaped weld design table. I circled the number close to 2,500KN, since the whole page could not be screen snapped.

 

[Agent666]

Ok, I was imagining the full return being welded, I see now what you mean from the 2D return! I thought you meant two dimensional.

Not sure I like it all the same with just the small return, the comments still apply to some degree, obviously with quite a long angle the secondary effects from moment/torsion on the weld group are somewhat reduced. If your beam has any tension its also quite a poor loadpath.

I assume the design method doesn't require the welds to the beam web in combination with the welds to the angles like shown on the left? Bolting it might invalidate the design method?

If you bolted it with slotted holes it will behave very different to welding the angles to the beam web as shown. Really wouldn't like that as you can imagine the angle legs prying off the web, placing the weld in bending (which is really undesirable in connection design).

 

[sunyaer]

The left shows the framing leg of the angles has welds, and the outstanding leg bolts to column web, which is the option you suggested. The right picture shows the option I used.

I think bolting on one leg provides more end rotation ductility for the beam, which is more desirable than welding framing leg and outstanding leg in a connection in the meantime.

Column web or beam web do you refer to in "angle legs prying off the web"?

 

[hoshang]

The only condition where I'd consider the effective length being 4.6m would be if the bottom flange of the beam was restrained in position via a fly brace system or similar depth beams in the orthogonal direction (or similar detailing)

If the fin plate is short, then one half of the bottom flange is removed to clear fin plate when lowering the beam into position. How fly brace system is set in this case?

 

[hoshang]

I followed the thread from the start. your comments are highly appreciated. Am I wrong when saying "If the fin plate is short, then one half of the bottom flange is removed to clear fin plate when lowering the beam into position. How fly brace system is set in this case?"

 

[Agent666]

Hi sorry for the delay in replying.

Column web or beam web do you refer to in "angle legs prying off the web"?

I was referring to the angle legs prying off the column web, if bolt holes are slotted in beam web, then bolt group cannot carry the moment, and the dubiously welded angles can pry off the column web at the top placing the welds in bending which should be avoided. This is why I was assuming based on the printout you gave that the design model you had used required welding to the beam web and not bolts, quite fundamentally different behaviour in the connection if you changed this detail (weld group between the beam web and angles can take the moment and is stiff, this is required to deliver a shear to the welds between angles and web, vs a moment and shear (resulting in tension at top of angles and possible bending in the welds)). Think of the welded angles to beam web as simply an extension of the beam, vs the angles being an extension to the column in what I understand to be your current proposal, its really about where the pin might be and the resulting design actions on the connection components. With fully welded angles, pin is pretty much at the column face (due to the flexibility of the angles and how they are welded only on the outer edge), vs slotted bolt holes and pin being at bolt line with correspondingly different moment acting on the angle/column web weld group with forces developing normal to the web.

How fly brace system is set in this case?

In the last scenario being discussed, the beam was being attached directly to the column web via fin plate with bolts to the beam web and some welds to the column web using angle brackets, in this scenario a fly brace would not be required for the columns stability (like it might have been required for the earlier scenario where the beam went over top of the column with a nominally pinned detail and could kick out sideways under load). I think the easier thing to do with the current scenario is to simply make sure that the fin/end plate satisfies the code requirement that if the fin plate/end plate is of a certain depth compared to the section depth then a certain degree of restrain can be achieved for the beam. I.e. avoid short fin plates. If you have flange on one side, you still have something similar to a channel, which doesn't have any special requirements. This is why I mentioned using an end plate rather than a fin plate as you can lower it into position without having to cope the beam, and bolt directly through the web, OP adopted another detail ultimately.